I think Newbies' just pointing out that many industries are making the process of tipping less voluntary. I would have to agree. If usually overtip at restaurants, but if they automatically add 15%, I don't tip a penny more. It's just the principle of it. I'm still of the old-school belief that tips should be a reward given, not automatically expected.
As for autotipping, it shouldn't matter to most people. The only reason for it is to make people actually go and ask to have it removed to avoid tipping. Not too many people would actually like to go and explain why they don't want to tip the waiter or the cabin steward, or whomever. If you always tip anyway, then the only thing it'll deprive you of is the satisfaction of handing over the envelope.
If you slip your waiter some extra cash, I have no doubt that it'll stay in his or her pocket. If you're going to overtip, you should probably do this instead of adjusting it on your account.